Homebrew PCBs

I know that iron salts are safe to dump (in reasonable concentrations), but 
that news about aluminum in the environment is good to know. So scrap iron 
it is. Small pieces are faster because increased surface area, but metal 
powder is definitely not required, steel food cans out of the trash bin do 
a perfectly fine job. Over the years I have dumped many liters of this 
neutralized precipitated etchant solution on my garden, with zero effect.

Steve,
  I should try write up a web page someday on treating etchants with scrap 
iron, but I would only doing this after getting more scientific results and 
doing a few experiments. I suspect the copper concentration in the solution 
after 1 week is under 100 ppm (%0.01 or 0.1 g/liter). I can test this by 
adding excess ammonium hydroxide and so any copper dissolved in there will 
form deep blue copper complex. Normally, in clear solutions a extreamily 
faint blue tint is visible at Cu concentrations around 10ppm. But the 
dissolved iron(II) ions forms cloudy yellow/brown iron(II) hydroxide with 
the ammonium hydroxide and makes it difficult see the blue shade. The 
ammonium hydroxide is only needed as a test to confirm the process is working.

Adam

Richard Mustakos wrote:
> Adam,
> Thanks for the info on slaked lime.
> But go with the iron: aluminum may be better at getting the copper out, 
> but when I asked a company that deals with powdered metals about the 
> toxic waste thing, they said that aluminum was considered more hazardous 
> then copper.  They said there were no restriction on copper for them, 
> but there were aluminum restrictions.
 > ....